The present invention relates to laser devices adaptable for optical communication, optical information processing or optical memories and more particularly relates to laser devices which are able to switch their oscillating wavelength.
Recently, in the case where computing or memorizing of optical information is required, it is necessary to convert light to electricity, and again, electricity to light. The conversions of light/electricity and electricity/light have been a problem for processing large amounts of information which involves light. Therefore, to reply to the requirements of opto-electronics, it is desired to develop optical information processors which can perform input-output operations with light itself. However, a practical device that can be used for such purposes has not been developed.
An opto-bistable semiconductor laser using a saturable absorber is known (for example, 1983 National Convention of the IEICE of Japan, p. 937, Odagiri et al). Nevertheless, in the case where a saturable absorber is used, there are problems, such as the device being unsuitable for high speed operation, and so on. This is because the response time is strictly determined by the lifetime of its spontaneous emission.
On the other hand, optical bistability between the traverse electric (TE) mode and the traverse magnetic (TM) mode in a buried heterostructure (BH) laser has been reported. ("Picosecond-Switching Optical Bistability in a TM-Wave Injected BH Laser", Extended Abstracts of the 18th (1986 International) Conference on Solid State Device and Materials, Tokyo, 1986, Y. Mori et al). In this report, a TM wave selected by means of a polarizer is injected into the facet of a InGaAsP laser .lambda.g 1.3 .mu.m) operating in a TE mode. In the light-output versus light-input characteristics of the laser, a hysteresis loop is observed. It has been confirmed that the laser operates in the TM mode at the higher state of the hysteresis loop and operates in the TE mode at the lower state. And, by removing the TM wave, the bistability between both modes disappears.
However, in each bistable state, there is a mixing of the TE mode and the TM mode. Thus, the extinction ratio is small. Further, because mixing occurs, it is not suitable for multi-mode optical communication, or optical information processing and so forth.
As another experiment concerning a semiconductor laser, there has been reported a phenomena that the peak of the oscillating wavelength of an AlGaAs laser is shifted as the temperature or its drive D.C. current changes ("Longitudinal-mode behaviors of mode-stabilized Al.sub.x Ga.sub.1-x As injection laser" M. Nakamura et al, J. Appl. Phys. 49(9), September 1978). And in this paper, a plurality of hysteresis loops (wavelength vs. temperature or dc current) have been observed along the temperature or the dc current direction.
Further, in the Japanese Patent disclosure (Kokai) No. 57-187983, Y. Yamamoto et al, there is shown an optical amplifier using a semiconductor laser. A laser is oscillated in a single longitudinal wavelength. When injection light having a wavelength that coincides with another longitudinal mode of the laser is injected, the oscillation wavelength changes to the wave injected as the intensity of the injected laser increases. The output light is then passed through a set of wavelength filters. However, this report does not show any detail of the apparatus or of the hysteresis. It is important to have an hysteresis characteristic for memories for computing and so forth.